This invention relates generally to golf balls having at least one intermediate layer that is a radially oriented, transversely isotropic composite. The intermediate layer is formed of two materials with different material properties so that the layer provides unique performance properties when the ball is struck with different clubs.
Generally, golf balls have been classified as wound balls or solid balls. Wound balls are generally constructed from a liquid or solid center surrounded by tensioned elastomeric material. Wound balls are generally thought of as performance golf balls and have good resiliency, spin characteristics and feet when struck by a golf club. However, wound balls are generally more difficult to manufacture than solid golf balls.
Early solid golf balls were generally two piece balls, i.e., comprising a core and a cover. More recently developed solid balls have a core, an intermediate layer and a cover, in order to improve the playing characteristics of the ball.
The prior art is comprised of a variety of golf balls that have been designed to provide particular playing characteristics. These characteristics are generally the initial velocity and spin of the golf ball, which can be optimized for various types of players. For instance, certain players prefer a ball that has a high spin rate in order to control and stop the golf ball. Other players prefer a ball that has a low spin rate and high resiliency to maximize distance. Generally, a golf ball having a hard core and a soft cover will have a high spin rate. Conversely, a golf ball having a hard cover and a soft core will have a low spin rate. Golf balls having a hard core and a hard cover generally have very high resiliency for distance, but are hard feeling and difficult to control around the greens. Various prior art references have been directed to adding an intermediate layer of core material or second cover layer to improve the playability of solid golf balls.
Golf ball manufacturers, however, are continually searching for new ways in which to provide golf balls that deliver good performance for golfers.
The present invention is directed to a golf ball with a core, a cover and an improved intermediate layer disposed between the core and the cover. The improved intermediate layer is a composite that is radially oriented and transversely isotropic. The layer provides unique performance properties when the ball is struck with different clubs.
In one embodiment, the improved intermediate layer is formed with a sufficient thickness to alter the playing characteristics of the ball and respond differently to different types of clubs. The material properties of the materials forming the improved intermediate layer are preferably selected such that the properties of the layer can be changed by varying the percentage of each of the constituents forming the layer or by changing the position, dimensions or configuration of the two materials with respect to each other.
One embodiment of the present invention is a golf ball having a core, a cover and an intermediate layer that is made of an interstitial material distributed throughout a binding material. The interstitial material may be distributed symmetrically within the layer, and more particularly may be spherically symmetric with the remaining parts of the ball. In addition, the interstitial material may be radially oriented or circumrferentially oriented.
In another embodiment, the ratio of the elastic modulus of the interstitial material to the elastic modulus of the binding material is about 3:1 or greater, while in another embodiment this ratio is between about 5:1 and about 10:1.
In yet another embodiment, the ratio of the interstitial material long-time shear modulus to the binding material long-time shear modulus is about 30:1 or less. It is preferred in one embodiment that the ratio of the interstitial material long-time shear modulus to the binding material long-time shear modulus is about 3:1 or greater, and even more preferably is between about 5:1 and about 10:1.
The intermediate layer may be of any desired thickness. In one embodiment, however, the intermediate layer has a thickness between about 0.080 inches and about 0.340 inches. More preferably, the intermediate layer is between about 0.125 inches and about 0.250 inches thick.
The interstitial material may be formed in any manner desired. In one embodiment, the interstitial material is formed of discrete pieces of material, while in another embodiment it is formed of a continuous piece of material. Preferably, the material that forms the interstitial material is a fiber or a plurality of fibers.
Portions of the intermediate layer may extend into the preceding (i.e., inner) or subsequent (i.e., outer) layer of the ball. In one embodiment, the interstitial material extends outward into the layer surrounding the outer surface of the intermediate layer, while in another embodiment the interstitial material extends inward into the material on the inner surface of the intermediate layer. In one embodiment, however, the layer surrounding the outer surface of the intermediate layer is a cover. In a preferred embodiment, the cover is separate from the intermediate layer so that no material from the intermediate layer extends into the inner surface of the cover.
In yet another embodiment, at least one intermediate layer has at least one material property in the radial direction that is different from that property in the circumferential direction. For example, the intermediate layer may have a material property in the radial direction that is larger than that property in the circumferential direction. One such material property may be the elastic modulus.